1. Field of the Invention
The present invention relates to a piezoelectric actuator suitable for driving an ink-jet head, and a method of manufacturing such a piezoelectric actuator.
2. Description of the Related Art
Ink-jet printers among non-impact printers progressively extending their market in recent years are based on the simplest principle and are suitable for color printing. The so-called drop-on-demand (DOD) ink-jet printers are favorites among ink-jet printers.
A previously proposed ink-jet head for printers of the aforesaid type employs, as a driving source, a laminated piezoelectric actuator formed by alternately laminating piezoelectric layers and electrodes. In this laminated piezoelectric actuator, the piezoelectric layers are distorted when a driving voltage is applied across the electrodes and thereby the volume of an ink chamber adjoining the actuator is changed. The distortion of the piezoelectric actuator increases in proportion to the number of the piezoelectric layers even if the driving voltage is low.
Various efforts have been made to provide an ink-jet head employing a piezoelectric actuator with a plurality of nozzles in a high density in order that a variety of characters can be printed with a high resolution.
For example, a print head disclosed in JP-A No. 4-1052 has an arrangement of piezoelectric elements formed by forming slits at fixed intervals in a sintered, laminated piezoelectric plate. The piezoelectric elements are distorted in directions perpendicular to the direction of polarization, i.e., in a mode corresponding to the piezoelectric strain constant d31, to control the pressure in a pressure chamber adjoining the piezoelectric element.
An ink-jet head disclosed in JP-B No. 4-52213 forms a piezoelectric element on a first electrode formed on one of the opposite sides of a wall defining an ink chamber and forms a second electrode on the other side of the wall for high-level integration and facilitating electrical connection of electrodes to the piezoelectric element.
In the prior art print head disclosed in JP-A No. 4-1052, however, the alternately arranged electrodes of different polarities are exposed on the cut surfaces of the piezoelectric elements formed by slitting the laminated piezoelectric plate. Therefore, there is the possibility that the electrodes are short-circuited by aqueous ink adhering to the cut surfaces or by moisture contained in the atmosphere and adhering to the cut surfaces of the piezoelectric elements.
Generally, the thickness of the piezoelectric layers is as small as about 0.02 mm and the thickness of the electrodes is as small as about 0.002 mm. Therefore, the electrodes are arranged at very small intervals. Moreover, the piezoelectric layers are compressed by a machining pressure applied to the piezoelectric plate when forming the piezoelectric elements and the thickness of the piezoelectric layers is further reduced. Consequently, there is the possibility that the intervals between the electrodes are reduced and the electrodes are short-circuited during manufacture.
In the prior art ink-jet head disclosed in JP-B 4-52213, the first and the second electrodes for electrically connecting the piezoelectric element are formed on the opposite sides of the piezoelectric element and are not included in a plane. Therefore, a complicated connecting structure is required for connecting the electrodes to an external circuit, which increases mounting cost and the size of the head is inevitably large.
When laminated piezoelectric elements are employed, the electrodes are exposed on cut surfaces similarly to those of the former ink-jet head and, therefore, there is the possibility that the adjacent electrodes are short-circuited.